In a conventional multi-domain vertical alignment (MVA) LCD, protrusions or slits on a color filter substrate or a thin film transistor (TFT) array substrate make liquid crystal molecules arrange in multiple directions. This creates different alignment domains which allow the conventional MVA LCD to have a wide viewing angle. However, the transmittance of the MVA LCDs changes along with the variation of the wide viewing angle, which results in a variation of gray level. In other words, when the viewing angle varies, the brightness of the MVA LCD changes, which causes color shift.
FIG. 1 is a characteristic curve diagram of voltage to transmittance of a conventional MVA LCD. Referring to FIG. 1, the curve 11 to the curve 13 indicates the light transmittance observed when viewing the MVA liquid crystal display panel from the front. The curve 11 is a transmittance of red light, the curve 12 is a transmittance of green light, and the curve 13 is a transmittance of blue light. However, when viewing the MVA LCD panel from an oblique angle (e.g., 60 degrees), under the same working voltage the observed light transmittance changes and drifts from the curves 11, 12, and 13 to the curves 14, 15, and 16 respectively.
It can be seen that in regions of a higher gray level and a lower gray level, the light transmittance of the curve 11 is approximate to that of the curve 14, the light transmittance of the curve 12 is approximate to that of the curve 15, and the light transmittance of the curve 13 is approximate to that of the curve 16. However, in the middle gray level region, the light transmittances of the curves 11, 12, and 13 are significantly different from those of the corresponding curves 14, 15, and 16. In other words, the color shift phenomenon of the higher and lower gray levels is slight, and the color shift phenomenon of the middle gray level is severe.
In order to eliminate or reduce the color shift phenomenon, the conventional art divides one pixel unit into two regions of different light transmittances. The light transmittance of one region is relatively higher, thus displaying the color of a higher gray level, and the light transmittance of the other region is lower, thus displaying the color of a lower gray level. The color of the higher gray level and the color of the lower gray level are then mixed into a color of a middle gray level. Therefore, regardless of whether the user views the improved MVA LCD panel from the front or at an oblique angle, he or she can view similar colors.
In order to achieve the above technology, CHIMEI Corporation has developed an MVA pixel structure (Taiwan Patent Application No. 93132909), as shown in FIG. 2. A protection layer 303 of silicon nitride covers a TFT array substrate 301. Next, transparent electrodes 305 and 307 are disposed on the protection layer 303, so as to divide the entire pixel region into display regions A and B. The transparent electrode 307 is electrically connected to the transparent electrode 309, and the transparent electrode 305 is floated to the transparent electrode 309. In addition, a liquid crystal layer 313 is filled between the TFT array substrate 301 and the opposite substrate 311.
It can be seen from FIG. 2 that in the display region A, since the electrode 307 is at the same potential as the source end 309, and a common electrode 315 on the opposite substrate may be connected to a common voltage, a liquid crystal capacitor 313a may be formed in the liquid crystal layer 313. In the display region B, a protection layer capacitor 303a may be formed in the protection layer 303 between the electrode 309 and the electrode 305. Similar to the display region A, a liquid crystal capacitor 313b is also formed between the electrode 305 and the common electrode 315.
FIG. 3 is an equivalent circuit diagram of the pixel structure in FIG. 2. Referring to FIGS. 2 and 3 together, a drain end of the TFT 321 is electrically connected to the data line 31, and a gate end is electrically connected to the scan line 33. Furthermore, a source end of the TFT 321 is electrically connected to the storage capacitor 323, the liquid crystal capacitor 313a in the display region A, the protection layer capacitor 303a, and the liquid crystal capacitor 313b in the display region B. The voltage of the liquid crystal capacitor 313a in the display region A is V1, and the voltages of the protection layer capacitor 303a and the liquid crystal capacitor 313b in the display region B are V2 and V3 respectively. Considering the voltages of the liquid crystal capacitors in the display region A and in the display region B are different, the light transmittances at each display region may be different. For example, display region A may have a high gray level and display region B may have a low gray level. Mixing the high and low gray levels may produce a middle gray level when viewing the MVA LCD panel from different angles.